Energy and Exergy Analysis for Hydrothermal Gasification Integrated with Anaerobic Digestion

Abstract

Anaerobic digestion (AD) of wet and low-grade biomass materials plays an important role in the transition to sustainable energy resources. However, challenges related to digestate management and feedstock scarcity still hinder its implementation. Digestate recycling via hydrothermal gasification (HTG) can help overcoming these challenges. However, HTG process is very energy sensitive and needs a good strategy of process and heat integration. In this work, pinch analysis is carried out to identify potentials for heat integration for an integrated system of HTG with AD. The heat exchanger system is subsequently optimized to achieve the minimum energy requirement (MER) determined from the pinch analysis. Furthermore, exergy analysis is implemented to pinpoint the thermodynamic inefficiencies of the unit operations within the process. It was found that process units with biochemical and chemical reactions, i.e., AD, HTG, and combustor contribute to the largest exergy destruction. In addition, the gas turbine and steam turbine systems also have low exergetic performance.